1. Field of the Invention
The present invention relates to a control system and method for automatically stopping and starting the engine of a vehicle, and in particular, to systems and methods for prohibiting the engine from being automatically stopped when the pressure in the fuel tank exceeds a predetermined pressure which is lower than atmospheric pressure.
2. Description of the Related Art
Conventionally, a control system for automatically stopping and starting the engine of a vehicle is known, in which the engine is automatically stopped when specific engine-stop conditions are satisfied, so as to reduce fuel consumption, and in which the engine is restarted under specific engine-restart conditions.
For example, Japanese Unexamined Patent Application, First Publication No. 2000-257462 discloses a hybrid vehicle, in which when the vehicle is driven at a low speed by selecting the D mode (i.e., drive mode) by using the select lever, the engine is automatically stopped if the vehicle is stopped while the driver is depressing the brake pedal. However, such automatic stop control is prohibited (i) during the warming up of the vehicle, (ii) during the operation of the air conditioner, (iii) when the electric load is large, or the like. In addition, the engine is restarted when the brake-master-power negative pressure reaches a specific pressure close to atmospheric pressure.
On the other hand, recently, various measures for preventing air pollution due to evaporating fuel have been proposed. For example, Japanese Unexamined Patent Application, First Publication No. Hei 10-299582 discloses a xe2x80x9cnegative-pressure and closed fuel tankxe2x80x9d system for preventing the evaporating fuel, generated in the fuel tank, from being discharged to the atmosphere. In this system, the fuel tank is connected via a canister to an air intake passage of the internal combustion engine and the pressure inside the fuel tank is maintained at a suitable negative pressure.
However, in the negative-pressure and closed fuel tank system, the pressure of the fuel tank is set to a specific level by using the negative pressure of the manifold at the intake side. Therefore, if such a negative-pressure and closed fuel tank system is applied to a vehicle having the control system for automatically stopping and starting the engine, then after the specific conditions are satisfied and the engine is stopped, the inner pressure of the fuel tank may be lower than a target level for a long time or may not reach the target level.
In order to solve this problem, the capacity of the canister must be increased so as to improve the absorbing capability of the evaporating fuel during the engine stop. Consequently, the weight of the vehicle also increases, and the flexibility in the arrangement of functional components in the vicinity of the canister is degraded.
In consideration of the above circumstances, an object of the present invention is to provide a control system and method for automatically stopping and starting the engine of a vehicle, so as to perform the automatic engine-stop and start control while the negative pressure of the fuel tank is maintained at a suitable level.
Therefore, the present invention provides a control system for automatically stopping and starting an engine (e.g., an engine E in an embodiment explained below) of a vehicle, comprising:
a fuel tank (e.g., a fuel tank 19 in the embodiment explained below) in which evaporating fuel is generated;
a canister (e.g., a canister 33 in the embodiment explained below) for absorbing the evaporating fuel generated in the fuel tank and purging the absorbed evaporating fuel into an air intake system of the engine;
a pressure control section (e.g., a tank pressure control valve 30 and an evaporating fuel passage 20 in the embodiment explained below) for controlling the inner pressure of the fuel tank in a manner such that the internal pressure is maintained at a predetermined level at least while the engine is operated, wherein said predetermined level is lower than the atmospheric pressure; and
an engine stop/start determining section (e.g., an engine ECU 1 in the embodiment explained below) for stopping or starting the vehicle according to the driving state of the vehicle, wherein the engine stop/start determining section determines to prohibit an engine stopping operation when the internal pressure of the fuel tank is higher than the predetermined level.
According to this structure, when the internal pressure of the fuel tank is higher than the predetermined level, the engine stop/start determining section determines to prohibit the engine stopping operation, so that the internal pressure of the fuel tank can be quickly reduced to the predetermined level which is lower than the atmospheric pressure. Therefore, it is possible to reliably prevent the evaporating fuel in the fuel tank from being discharged to the atmosphere (i.e., outside air).
The engine stop/start determining section controls stopping or starting of the vehicle according to the driving state of the vehicle. Therefore, the engine is stopped under specific conditions, for example, when (i) the starting operation using the motor is possible (e.g., in the determination of step S106 in the embodiment, the value of a motor start permission determination flag F_MOTSTB is 1), (ii) the SOC of the battery (corresponding to the remaining battery charge) is not within an over discharge range (e.g., in the determination of step S107 in the embodiment, the value of an energy storage zone determination flag F_ESZONE is 0), and (iii) the engine water temperature is equal to or above a predetermined temperature (e.g., in the determination of step S108 in the embodiment, the engine water temperature TW is equal to or above a lower limit water temperature TWFCMG).
Typically, the engine stopping operation includes fuel cut during deceleration. The fuel cut during deceleration is terminated under specific conditions. When the conditions for stopping the engine are satisfied (e.g., the value of an engine stopping control execution flag F_FCMG is 1 in the embodiment explained below), the fuel cut is continued. Due to the continuation of the fuel cut, the engine load may be low and it may be difficult to maintain the negative pressure of the fuel tank at a suitable level. In this case, a suitable negative pressure of the fuel tank can be obtained by restarting the engine.
Typically, when the engine is being stopped due to the determination of the engine stop/start determining section, the engine stop/start determining section determines to start the engine if the internal pressure of the fuel tank exceeds the predetermined level.
Accordingly, when the engine is being stopped by the control system for automatically stopping and starting the engine, the engine stop/start determining section determines to start the engine if the internal pressure of the fuel tank exceeds the predetermined level. Therefore, the internal pressure of the fuel tank can be quickly reduced to the predetermined level which is lower than the atmospheric pressure. Therefore, it is possible to reliably prevent the evaporating fuel in the fuel tank from being discharged to the atmosphere.
The control system for automatically stopping and starting the engine may further comprise:
a section for detecting an amount of evaporating fuel absorbed into the canister, wherein:
the engine stop/start determining section determines to prohibit an engine stopping operation when the detected amount of evaporating fuel absorbed into the canister is equal to or above a predetermined level. Accordingly, the purging operation of the evaporating fuel from the canister to the engine is continued so that the concentration of the evaporating fuel in the canister can be reduced and the internal pressure of the fuel tank can be maintained at the predetermined level lower than the atmospheric pressure. Therefore, it is possible to reliably prevent the evaporating fuel, which cannot be absorbed into the canister, from being discharged to the atmosphere.
The present invention also provides a control method of automatically stopping and starting an engine of a vehicle which has a canister for absorbing evaporating fuel generated in a fuel tank and purging the absorbed evaporating fuel into an air intake system of the engine, the control method comprising:
a pressure control step of controlling the inner pressure of the fuel tank in a manner such that the internal pressure is maintained at a predetermined level at least while the engine is operated, wherein said predetermined level is lower than the atmospheric pressure; and
an engine stop/start determining step of stopping or starting the vehicle according to the driving state of the vehicle, wherein the engine stop/start determining step includes determining to prohibit an engine stopping operation when the internal pressure of the fuel tank is higher than the predetermined level.